A study of the potentiometric behaviour of aqueous solutions of weak amphoteric polymers was carried out in advance of an investigation of weak polyamphoteric membrane prepared from a mixture of the amphoteric chitosan and poly(vinyl alcohol). Carboxymethyl chitosan and succinyl chitosan were used as weak polyampholytes. Succinyl chitosan is composed of amino and carboxyl groups, which were provided by substitution of the former with the latter. The portion of substituted groups from amino to carboxyl is represented by the degree of substitution (DS). Potentiometric titrations were performed with added salt of the 1-1 type or 2-1 type and without added salt. The behaviour could be rationalized through the dissociation mode concept based on a modified Henderson-Hasselbalch relationship.